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Heat and Color

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Joined: 01 Jun 2010
Posts: 1
Location: SaudiArabia

PostPosted: Tue Jun 01, 2010 5:08 pm    Post subject: Heat and Color Reply with quote

Umm, I need help in a physics project. I'm just wondering about something that I have to know about before proceeding with my conclusions and analysis to base them on my understanding of it. It's about color and heat absorption. I tried looking for helpful info on the internet and didn't find anything useful. My physics teacher couldn't help me either and told me to find someone else who might know more about this topic. I thought maybe you can help!

Let's say we have two objects, a blue object and a red one, both left in the sun. The blue object became warmer than the red; because it absorbed more light energy that transformed into heat. How do I to explain the relation between color and heat? Why does color blue heat more in the sun?
When I thought about the difference between red and blue, blue's wave frequency is higher than red, making it contain more energy than red. However, the confusing part comes when we consider the fact that blue REFLECTS its high energy wave (which is why we see it as blue), while red reflects low energy. So basically, red absorbs higher light frequencies (including the high frequency of the color blue) than blue, yet blue (that reflects color blue with its high energy) still absorbs more energy and heats up more.

I want to know if my analysis is correct, because in case I'm right and red IS supposed to absorb more energy, I can explain it using the fact that with light scattering of the sun. Blue is the least color that reaches Earth, so the red object doesn't have much to suck from the blue's high energy wave frequencies coming from sun light anyways, and therefore blue is left to absorb the large amount of red and yellow beams and just reflects the "limited" blue contained in sun light!

Oh and one more thing, I asked about this in Yahoo answers, and someone told me that the higher the frequency of the color reflected, the more heat it can absorb. This, however, doesn't make any sense since color black that absorbs the most energy out of all colors reflects no colors at all, as opposed to white..

So, could anyone help me? I'm kinda stuck in the project and I want to check if I'm on the right track. I'd really appreciate it if you can help me figure this out! If you can tell me about your own thoughts, direct me to someone who can help, or tell me about a useful site that would help me specifically in this project, please tell me. I desperately need help..
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Joined: 23 Jun 2007
Posts: 125

PostPosted: Tue Jun 01, 2010 8:42 pm    Post subject: Reply with quote

This is an interesting problem. If the spheres are being heated by the Sun, then there is a whole spectrum of frequencies that are incident on the two spheres not just those due to visible light. There are the infra-red waves, which may cause resonance with the molecules in the material. Then there are the ultra violet frequencies, which have a higher energy per photon. The energy relationship is:

E = h f, where h is Planck's constant and f is the frequency.

So while the red ball it absorbs the higher frequencies, it is reflecting the red light. The blue ball reflects the blue light which has a higher energy per photon but when you sum the energy over all the frequencies the blue ball has turned more of the incident radiation into heat.
A black ball would absorb the most energy because it is absorbing the spectrum of frequencies that are incident on it.
I hope that helps.
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